earthlight

Nice comparison Tom. The striking thing to me here is that a total split of the vortex, or a SSW by definition is not really needed. We are already seeing the proverbial plant rising through the dirt from the seeds planted with the initial major tropospheric disruptions in November. Almost all models now agree on the development of a major stratospheric high over Western North America and a major displacement and stretching of the SPV. This should serve to enhance the potential for major blocking and a chaotic, stormy and cold pattern in the Eastern US.

I will not let you down. Give it some time still, but it will happen.

Nice to see higher heights poking into Greenland as well, concurrent with the continually disrupted SPV/TPV. Cross sections showed a nice tropospheric blocking signal on the GFS over Greenland and the N Atlantic.

Major L

I noticed this also

As others have discussed, the effects of the SPV being over Greenland are different than the TPV being over Greenland. The relationship between the stratosphere and troposphere is not always coupled, direct, linear etc. I wouldn’t look at the 10hPa graphics and suggest there won’t be a -NAO at 500hPa. Two totally different things.

Can you go into further detail about what meteorological elements suggest to you that the setup from 12/24 through 12/27 could rival Boxing Day, other than something that operational weather models have shown?

This is a silly statement to make considering any potential system is 350 hours away and this is one of NYC's top snowstorms of all time. Also the Boxing Day Blizzard was in 2010.

Posting this in here because I feel it may be of interest to many

Some fantastic thoughts in here, and I think many of us are in good agreement on the overall evolution of the pattern, I think in particular @Isotherm and I have never quite agreed to this distinct level on the likelihood of cold and snow. There is a harmony developing between many global forcing mechanisms and pattern drivers - from the lower levels of the atmosphere all the way into the stratosphere - and we continue to see signs of it in the medium to long range. Coming in to this winter, the stratosphere was a major uncertainty. We understood that there was a higher likelihood that the vortex would be weaker than normal, but with the QBO in flux it was always a bit of a wild card how the vortex would behave. The state of the vortex as we type today on 12/11/2018 is far beyond where I even thought it would be. It is weak, it is displaced, and it has been continually stretched. Almost all ensembles indicate that the vortex will approach the minimum range of climatological strength over the next two to three weeks, which is when the vortex is typically beginning to approach its climatological peak strength. This is significant in its own right. The harmonious and continuous Wave 1/Wave 2 hits to the vortex continue, and we are now on our fourth recurring Scandinavian ridge anomaly. The Wave 1 and Wave 2 hits have not quite been at ideal sync yet, but they have done their damage. There is excellent ensemble agreement that the subsequent Wave 1 hits near Christmas will deliver a significant blow to the stratospheric polar vortex, with a major warming event and very high anomalies near the pole. 45-75N heat flux forecasts are into the 10% range on the latest forecasts. This is not insignificant. The stratosphere is going to become a major influencer on the weather pattern, and high latitude ridging should become increasingly prevalent. We have seen some dissonance from the Pacific over the past two weeks and this is largely expected to continue into the period around 12/20. However, thereafter the agreement builds substantially that the Pacific jet should retract and even maintain significant poleward reach. Tropical forcing and global forcing from Asia aligns during this time as well. This leads us to a potential "goldilocks zone" from 12/25 onward, give or take a few days. At this time the potential rises notably for unusually cold air to move southward into Canada. There may be a brief lag as Canada had undergone a period of notable moderation in the weeks prior. However, between 12/25 - 1/5 there is increasing likelihood that deep cold will move southward as a larger -EPO ridge builds from British Columbia into the Arctic regions. It is not lost on me that the Atlantic will be significant as well - and the exact evolution of the stratosphere remains indeterminate at this time. However, it is my opinion that Atlantic high latitude blocking should become increasingly likely as that time frame goes on and we move into the first and second week of January. With a large scale ridge building poleward into Western Canada and Atlantic ridging becoming more notable (particularly into Greenland), the chances of cold and snow in the Eastern United States should begin to increase substantially. The potential exists for a memorable period of cold and winter weather potential during this general time frame. I am not comfortable forecasting more specific dates at this time, but the harmony of the above features leads me to believe that the likelihood of either a memorable period and/or winter storm(s) comes to a gradual crescendo during the period between 12/25 and 1/15 across the Eastern United States, particularly from the Northern Mid-Atlantic into New England.

I think the GFS is a bit fast with this overall evolution. But it's an OP model run at the long range - so that's not the point. But I think it's a little rushed.

Even if there is a trough in a west, it's less of a death wish when the Pacific jet is retracted, the EPO ridging is high and the heights are building into the higher latitudes..IMO

Even if that occurs, though, I feel as if such an event would only help in the long run, with continued flux into the Atlantic blocking domain, further pulling the rug out of the Atlantic pattern. By the way, the ECMWF EPS and GEFS 12z analogs for the 16-20 day period are insanely cold especially in the Central USA. A massive -EPO signal and major cold air dumping into Canada and the USA.

This is a situation where you have to continue to ignore the ensemble mean's smoothed values being depicted across the Lower 48, and instead take note of the trends occurring in the higher latitudes. Forecast model guidance will continue to adjust and pick up on the effects of the stratospheric evolution - allowing for the development of high latitude blocking with increasing vigor and breadth, both on the Pacific and Atlantic sides. We can see this process beginning as a trough digs into the Aleutians and a large-scale ridge builds from British Columbia northward towards the poles and into the Arctic regions. This poleward ridge is being heavily signaled over 300 hours in advance by a major 51-member ensemble mean. This is not by chance. I expect further adjustments of the height field in a positive direction in both the EPO and NAO domains, particularly both near British Columbia and Greenland, as we approach the period post 12/25 over the next week or so. Don't hold your breath for ensemble guidance to pick up on this soon, either. It will likely be several more days, perhaps not until next week, that guidance starts to see the fruits of the stratospheric displacement and major wave disruptions influencing the pattern more heavily.